Use of satellite soil moisture to diagnosis climate model representations of European air temperature-soil moisture coupling strengths

Authors: DONG, J - US Department Of Agriculture (USDA); Crow, Wade

Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2018
Publication Date: 11/8/2018
Citation: Dong, J., Crow, W.T. 2018. Use of satellite soil moisture to diagnosis climate model representations of European air temperature-soil moisture coupling strengths. Geophysical Research Letters. 45:12884–12891. https://doi.org/10.1029/2018GL080547.
DOI: https://doi.org/10.1029/2018GL080547

Interpretive Summary: During the summertime, soil moisture and air temperature have a coupled relationship such that a decrease in soil moisture leads to an increase in near-surface air temperature (which, in turn, leads to a further decrease in soil moisture). Constructing models that accurately represent this feedback is important for efforts to better predict the frequency of future heatwaves and droughts. In the past, efforts to improve models in this regard have been hampered by limitations in the quality of large-scale soil moisture data sets and our inability to establish a robust observational benchmark for the strength of the soil moisture - air temperature feedback. However, newly available, multi-year soil moisture data sets acquired from the NASA Soil Moisture Active/Passive (SMAP) mission provide an opportunity to bridge this gap. In this paper, we demonstrate that SMAP soil moisture products reveal a tendency for climate models to underestimate the strength of the summertime soil moisture - air temperature feedback in Europe. Since this feedback is known to increase the magnitude of summertime air temperature variability, these results suggest that climate models are generally underestimating the frequency of European heatwaves and droughts in future climate projections. On-going work is attempting to extend these findings to the United States Corn Belt.

Technical Abstract: The interaction between soil moisture and air temperature is a key factor affecting variability in European summer daily maximum air temperatures. Therefore, climate models which accurately represent soil moisture - air temperature coupling strengths are more likely to correctly project the future frequency of European heat waves. However, modeled estimates of soil moisture - air temperature coupling strengths contain large uncertainties and inter-model differences, and general circulation models (GCMs) are hypothesized to generally underrepresent European land-atmosphere coupling. However, due to a lack of spatially extensive ground-based soil moisture observations, model-based predictions of soil moisture - air temperature coupling strengths have not been adequately verified. Here, we utilize remotely sensed soil moisture products to evaluate soil moisture – air temperature coupling strength estimates provided by seven Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models. Soil moisture retrievals provided by the NASA Soil Moisture Active/Passive (SMAP) mission are shown to be uniquely suited for this type of verification. Based on comparisons to SMAP-based coupling values, we demonstrate that CMIP5 models generally underestimate soil moisture-air temperature coupling strengths - particularly in central Europe. This provides new observational evidence for a low bias in GCM representation of European soil moisture - air temperature coupling.